Embedded computer controller systems are becoming increasingly prevalent in a variety of household and office devices. These devices include appliances, speech communications systems, environmental control systems, security monitoring systems and more. For these embedded controllers to be useful, they must communicate with each other and, with a centralized control and monitoring system operated by a human user. One possible communications medium is the electrical wiring that already exists within these buildings.
The prior art describes devices for achieving bi-directional communications between intelligent systems using the electrical power distribution wires contained in homes or office buildings. The prior art also describes methods of enhancing the communications by filtering noise caused by transient electrical surges or power spikes that interfere with the quality of communications, in both analog and digital devices.
In U.S. Pat. No. 5,805,053, issued Sep. 8, 1998, and incorporated herein by reference, C. H. Patel et al., describe an appliance adapted to transmit and receive information signals using the same electrical wiring that power the appliance. In U.S. Pat. No. 4,398,178, issued Aug. 9, 1983, and incorporated herein by reference, A. Russ et al. describe another method for achieving communications between devices by using power lines.
In U.S. Pat. No. 5,684,450, issued Nov. 4, 1997, and incorporated herein by reference, P. A. Brown, describes a method and apparatus for using the lines of a power transmission network to transmit and receive voice and digital data to and from remote locations. Brown suggests using available frequency bands between 1 MHz and 60 MHz. Brown also suggests that reliable analog and digital communications of wide bandwidth may be achieved along long distances using internal and external electrical lines of a building.
There are drawbacks, however, in communicating along existing power lines. Power lines as a communications medium lack security and privacy. All buildings, including houses and offices, are connected to a local electric utility and are, consequently, directly connected (i.e., dotted) together. Furthermore, all rooms within a house, apartment building, or office building are also directly connected together. This poses several problems. First, communications between devices may be monitored or intercepted by unauthorized users. Second, one device may interfere with another device, either intentionally or unintentionally. Third, the amount of communications traffic may overwhelm the bandwidth available along the electrical wiring. The prior art has attempted to eliminate some of these problems by encoding or encrypting communications between devices. These solutions, however, increase cost and complexity of the device, and do not address the bandwidth problem.
In U.S. Pat. No. 5,365,154, issued Nov. 15, 1994, and incorporated herein by reference, J. K. Schneider et al. describe a device for communicating along power transmission lines. The described device includes a means for applying an identification code to the device, so that the device may be controlled individually from a central location. By including address information with the control and data information, each device or a group of devices may selectively respond. Adding address information to the data, however, is an inadequate solution to achieving security and privacy in communications. First, cooperation between devices is necessary by selecting a unique address from a group of addresses to identify a particular device. Second, all data information sent along the power lines is detectable by other devices beyond the intended device or group of devices. Third, the data information is subject to interference from another device that is also communicating along the same power lines.
In U.S. Pat. No. 4,429,299, issued Jan. 31, 1984, and incorporated herein by reference, J. M. Kabat et al., describe a two-way power line communications system, shown as FIG. 1 in the patent and reproduced herein as FIG. 1. Referring now to FIG. 1, there is shown a room status indication system, designated generally as 16, which uses existing power lines for communications. The heart of the system is processor 10. The processor is coupled to several data terminals, one of which is designated as 12, a status board 14, and a general purpose interface 24. The processor is capable of communicating with each room in a building or a building complex that is equipped with a room control unit. Three such rooms are shown and generally designated as 18, 20 and 22. As represented by room 20, each room control unit includes receiver 26 and transmitter 28. Receiver 26 accepts and decodes interrogation and data signals from processor 10, and transmitter 28 encodes and sends return signals to processor 10. Each room control unit is capable of monitoring various conditions within the room. The room control unit is arranged to monitor room status, the condition of a smoke detector device, or any other activity that is capable of being initiated upon closure of a switch, such as activating a wake up message or providing a message waiting indication.
Each room control unit is equipped with circuitry for receiving from the processing unit an interrogation signal that includes data and address codes. The room control unit compares the address code with a pre-selected address code programmed into the unit. If the address code matches the pre-selected address, the room control unit performs an instructed command and responds appropriately. While the system described by Kabat et al. may function properly within a cooperating network, the system is susceptible to interference from non-cooperating systems that operate outside of the network. Any non-cooperating system that has access to the power lines is capable of detecting the signals being sent along the power lines. The non-cooperating system may also cause interference to the cooperating network by jamming the power lines, intentionally or unintentionally, with interfering signals.
As time progresses, increasing number of intelligent devices may be communicating important command and control information, and private sensitive data, along the power lines. Furthermore, more and more of these intelligent devices may be located in close physical proximity, such as in neighboring homes, apartments and office buildings. No prior art has suggested a suitable method or device to separate communications transmitted along power lines into distinct physical communication domains, so that communications within one network may be secure and private from communications within another network.